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Can you install a DI in an old tube head?

Discussion in 'Amps and Cabs [BG]' started by Greyvagabond, Apr 16, 2019 at 7:04 PM.

  1. Greyvagabond

    Greyvagabond Supporting Member

    Aug 17, 2007
    Los Angeles
    So I have an old and fairly rare Ampeg SVT-100 head. It sounds lovely! Unfortunately, it doesn't have a DI, because it is very old and was made on the cheap during one of Ampeg's numerous corporate transitions.

    I'm been GAS'ing for one of the small Ampeg portaflex amps, the PF-20t and PF-50t, mostly because they have the cool "transformer DI" that you can run (1) without a speaker and (2) after the power amp transformer, so it sounds more like the full amp's section. I also just got done recording on a vintage B-15 and desperately want to be able to take that sound with me.

    Is there anyway to higher an amp tech to retrofit a similar set-up into my SVT-100? Obviously, the cheapest answer is "buy a DI and take it with you, then plug the effects out into the DI" but my head doesn't even have a pre-amp out, so there's no way to get ANY of the amp's sound/mojo into a DI.

    Thoughts TB community? Doable or nah?
  2. JKos


    Oct 26, 2010
    Torrance, CA
    Are you wanting to do this silently or with a cab going? There are DIs designed to accept speaker level inputs.

    - John
    BasturdBlaster and Greyvagabond like this.
  3. I think you could likely buy a pf50t and a pizza with what that would cost to do properly.
  4. Cheap options:
    Silent recording, not happening.
    With cabinet, CountryMan 85 on speaker mode.
  5. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    A 200 watt dummy load resistor isn’t too bad, that plus the countryman gets you a silent recording mode. Alternatively a 200 watt capable dummy load/line out box like the rivera mini rock crusher can work, but you could buy a couple countrymans for that price.
    Rabidhamster likes this.
  6. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    Countryman Type 85 and several Radial DI boxes have a feature called "speaker level" DI.

    You run a speaker cable from the output of your amp to the DI box. You run a speaker cable from the DI to your cab. You run the XLR out from the DI box to the board.

  7. Wasnex


    Dec 25, 2011

    From what I understand the SVT100 is setup more like a Marshall, so it's not going to sound like the typical Ampeg.

    IMHO, it's not worth the expense or effort to have a DI installed as plenty of DIs can be configured to work at speaker level. Examples include the Countryman Type-85 and Radial JDI. The Radial manual specifies that you must engage a pad and a speaker emulation switch. The speaker emulation is basically a bandpass filter designed to mimic the response of a 12" guitar speaker. Some bass players have reported favorable results.

    A DI does not provide a load for the amp, so you still need to connect a speaker. If you want silent recording capability you need a load box. I have an Aracom PRX150-DAG attenuator that would be suitable and can be configured for silent recording, but it is not cheap. Destroy All Guitars - Aracom-DAG Power Attenuator You could also fabricate a dummy load using some big power resistors. I have seen these listed on Amazon and Ebay: http://www.electronics-salon.com/index.php?route=product/product&product_id=55808&search=dummy+load

    FYI. The PF20T and PF50T have built in dummy loads.
  8. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    ANything can be fixed. Is it worth it?

    The SVT-100 has a lot of space in the chassis. One could be retrofit. The question is, do you want pre-amp out to DI or powewr amp out to DI. The latter takes into account the power amp tone.

    If you want to create a pre-amp out, it would be a good idea to add an extra preamp tube, a post EQ gain makeup, and a cathode follower. Not difficult but a lot of tech time, it expense. The pre-out can be fed into a DI box.

    A DI connected to the power amp out is easier. As mentioned, you'd need a DI that is designed to connect to the power amp output. BUT you would need either a speaker load box, OR have a speaker cab connected and active . The DI would be daisy chained to the speaker cab ir power amp output.

    I think that this is your best option. The DI can be used with other amps. You don't want it built into the amp chassis.

    A third option. A DI with a built in load box that you use with your amp. This is doable because the SVT100 output is only 100W. You do not need your speaker cabinet connected with a load box.

    Here's two examples:

    Expensive ($800) but very good, interfaces to your computer for recording. Two notes Audio Engineering - Torpedo Live - Digital Loadbox

    Less expensive ($250 US): Two notes Audio Engineering - Torpedo Captor

    There are many similar products. Some sound better than others.

    Schematic attached.

    SVT100 gut shot.
    SVT100 gut shot.

    Attached Files:

    Last edited: Apr 17, 2019 at 8:32 AM
  9. typo?
    beans-on-toast likes this.
  10. Greyvagabond

    Greyvagabond Supporting Member

    Aug 17, 2007
    Los Angeles
    Much obliged. I forgot that the Countryman can be used with a speaker out. I think my cheapest solution is velcroing the damn thing inside the chassis and bringing the right cable to gigs.

    ...and maybe grabbing a pf20t also because those things are so damn cute!
    Microbass, Caca de Kick and Wasnex like this.
  11. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Thanks, I corrected it.
  12. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    If you go the Velcro route, use 3M Dual Lock instead.
    Mugre and Greyvagabond like this.
  13. Greyvagabond

    Greyvagabond Supporting Member

    Aug 17, 2007
    Los Angeles
    Thanks for the gut shot! It is such a simple-looking amp.
    beans-on-toast likes this.
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Anything is possible with the right skill set and understanding of the challenges. Just because it's possible doesn't make it entirely practical though.
  15. Greyvagabond

    Greyvagabond Supporting Member

    Aug 17, 2007
    Los Angeles
    Yup, I figured the answer was "sure, with an unlimited budget and willing, experienced amp tech." Just figured I'd see if anybody had ACTUALLY done something similar. The Countryman DI sounds like what I'm looking for.
    Wasnex likes this.
  16. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    I have done things like this many times, mostly for pro players in the touring industry where cost is secondary. That said, I do have the expertise, fully understand the challenges and have an extensive R&D lab and resources where I can do pretty much anything I want to. It's the same lab where I design new products, I design and build up amps from scratch all the time.

    Practical to a touring pro with an "unlimited budget" is likely going to be different than for an average player. If you have $1k, I'll take care of your amp for you ;)
  17. Greyvagabond

    Greyvagabond Supporting Member

    Aug 17, 2007
    Los Angeles
    That's actually not as bad as I was originally thinking! Hard for me to justify now but let's see what happens when this new record comes out.

    Thanks as always for sharing your wealth of knowledge.
    Al Kraft, Clutchcargo and agedhorse like this.
  18. theretheyare

    theretheyare Supporting Member

    Sep 4, 2010
    Brooklyn, NY
    Endorsing: Arkham Vacuum Tube Amplification
    It's one of the main reasons I purchased my Arkham Abyss pre, which basically is a B15 in a box and the "DI out" sounds fantastically deep and fat. Not sure if Micah still features these, but feel free to hit him up and ask him what he can do, he builds everything one at a time and is quite open to mods and customizing anyway. I thought the price to be super fair for the true tube tone and quality I got. ARKHAM
    Greyvagabond likes this.
  19. Greyvagabond

    Greyvagabond Supporting Member

    Aug 17, 2007
    Los Angeles
    I've been side-eyeing those Arkham pres for a long time. Their Beast of Both Worlds seems like a great one-box solution. I don't want to sell the Ampeg, but at close to 70 lbs its such a bear to take anywhere I find myself barely using it (especially when there is some doubt about how to mic my cab/grab a good-sounding DI).

    If he does custom work, I'd LOVE his simple Bullet pre attached to a 100-watt tube power section.
  20. iiipopes

    iiipopes Supporting Member

    May 4, 2009
    You are better off with one of the good digital emulators that you can feed it and get a line out of it into your amp, like a Line6 Bass POD. That way you have the "clean" version of your amp going to the house sound system and still have your backline amp/speaker setup. Please don't mod the head. You will ruin its value.
    seamonkey likes this.

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